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1 | /* |
2 | * Fast Userspace Mutexes (which I call "Futexes!"). |
3 | * (C) Rusty Russell, IBM 2002 |
4 | * |
5 | * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar |
6 | * (C) Copyright 2003 Red Hat Inc, All Rights Reserved |
7 | * |
8 | * Removed page pinning, fix privately mapped COW pages and other cleanups |
9 | * (C) Copyright 2003, 2004 Jamie Lokier |
10 | * |
11 | * Robust futex support started by Ingo Molnar |
12 | * (C) Copyright 2006 Red Hat Inc, All Rights Reserved |
13 | * Thanks to Thomas Gleixner for suggestions, analysis and fixes. |
14 | * |
15 | * PI-futex support started by Ingo Molnar and Thomas Gleixner |
16 | * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> |
17 | * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> |
18 | * |
19 | * PRIVATE futexes by Eric Dumazet |
20 | * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com> |
21 | * |
22 | * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com> |
23 | * Copyright (C) IBM Corporation, 2009 |
24 | * Thanks to Thomas Gleixner for conceptual design and careful reviews. |
25 | * |
26 | * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly |
27 | * enough at me, Linus for the original (flawed) idea, Matthew |
28 | * Kirkwood for proof-of-concept implementation. |
29 | * |
30 | * "The futexes are also cursed." |
31 | * "But they come in a choice of three flavours!" |
32 | * |
33 | * This program is free software; you can redistribute it and/or modify |
34 | * it under the terms of the GNU General Public License as published by |
35 | * the Free Software Foundation; either version 2 of the License, or |
36 | * (at your option) any later version. |
37 | * |
38 | * This program is distributed in the hope that it will be useful, |
39 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
40 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
41 | * GNU General Public License for more details. |
42 | * |
43 | * You should have received a copy of the GNU General Public License |
44 | * along with this program; if not, write to the Free Software |
45 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
46 | */ |
47 | #include <linux/slab.h> |
48 | #include <linux/poll.h> |
49 | #include <linux/fs.h> |
50 | #include <linux/file.h> |
51 | #include <linux/jhash.h> |
52 | #include <linux/init.h> |
53 | #include <linux/futex.h> |
54 | #include <linux/mount.h> |
55 | #include <linux/pagemap.h> |
56 | #include <linux/syscalls.h> |
57 | #include <linux/signal.h> |
58 | #include <linux/export.h> |
59 | #include <linux/magic.h> |
60 | #include <linux/pid.h> |
61 | #include <linux/nsproxy.h> |
62 | |
63 | #include <asm/futex.h> |
64 | |
65 | #include "rtmutex_common.h" |
66 | |
67 | int __read_mostly futex_cmpxchg_enabled; |
68 | |
69 | #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8) |
70 | |
71 | /* |
72 | * Futex flags used to encode options to functions and preserve them across |
73 | * restarts. |
74 | */ |
75 | #define FLAGS_SHARED 0x01 |
76 | #define FLAGS_CLOCKRT 0x02 |
77 | #define FLAGS_HAS_TIMEOUT 0x04 |
78 | |
79 | /* |
80 | * Priority Inheritance state: |
81 | */ |
82 | struct futex_pi_state { |
83 | /* |
84 | * list of 'owned' pi_state instances - these have to be |
85 | * cleaned up in do_exit() if the task exits prematurely: |
86 | */ |
87 | struct list_head list; |
88 | |
89 | /* |
90 | * The PI object: |
91 | */ |
92 | struct rt_mutex pi_mutex; |
93 | |
94 | struct task_struct *owner; |
95 | atomic_t refcount; |
96 | |
97 | union futex_key key; |
98 | }; |
99 | |
100 | /** |
101 | * struct futex_q - The hashed futex queue entry, one per waiting task |
102 | * @list: priority-sorted list of tasks waiting on this futex |
103 | * @task: the task waiting on the futex |
104 | * @lock_ptr: the hash bucket lock |
105 | * @key: the key the futex is hashed on |
106 | * @pi_state: optional priority inheritance state |
107 | * @rt_waiter: rt_waiter storage for use with requeue_pi |
108 | * @requeue_pi_key: the requeue_pi target futex key |
109 | * @bitset: bitset for the optional bitmasked wakeup |
110 | * |
111 | * We use this hashed waitqueue, instead of a normal wait_queue_t, so |
112 | * we can wake only the relevant ones (hashed queues may be shared). |
113 | * |
114 | * A futex_q has a woken state, just like tasks have TASK_RUNNING. |
115 | * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0. |
116 | * The order of wakeup is always to make the first condition true, then |
117 | * the second. |
118 | * |
119 | * PI futexes are typically woken before they are removed from the hash list via |
120 | * the rt_mutex code. See unqueue_me_pi(). |
121 | */ |
122 | struct futex_q { |
123 | struct plist_node list; |
124 | |
125 | struct task_struct *task; |
126 | spinlock_t *lock_ptr; |
127 | union futex_key key; |
128 | struct futex_pi_state *pi_state; |
129 | struct rt_mutex_waiter *rt_waiter; |
130 | union futex_key *requeue_pi_key; |
131 | u32 bitset; |
132 | }; |
133 | |
134 | static const struct futex_q futex_q_init = { |
135 | /* list gets initialized in queue_me()*/ |
136 | .key = FUTEX_KEY_INIT, |
137 | .bitset = FUTEX_BITSET_MATCH_ANY |
138 | }; |
139 | |
140 | /* |
141 | * Hash buckets are shared by all the futex_keys that hash to the same |
142 | * location. Each key may have multiple futex_q structures, one for each task |
143 | * waiting on a futex. |
144 | */ |
145 | struct futex_hash_bucket { |
146 | spinlock_t lock; |
147 | struct plist_head chain; |
148 | }; |
149 | |
150 | static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS]; |
151 | |
152 | /* |
153 | * We hash on the keys returned from get_futex_key (see below). |
154 | */ |
155 | static struct futex_hash_bucket *hash_futex(union futex_key *key) |
156 | { |
157 | u32 hash = jhash2((u32*)&key->both.word, |
158 | (sizeof(key->both.word)+sizeof(key->both.ptr))/4, |
159 | key->both.offset); |
160 | return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)]; |
161 | } |
162 | |
163 | /* |
164 | * Return 1 if two futex_keys are equal, 0 otherwise. |
165 | */ |
166 | static inline int match_futex(union futex_key *key1, union futex_key *key2) |
167 | { |
168 | return (key1 && key2 |
169 | && key1->both.word == key2->both.word |
170 | && key1->both.ptr == key2->both.ptr |
171 | && key1->both.offset == key2->both.offset); |
172 | } |
173 | |
174 | /* |
175 | * Take a reference to the resource addressed by a key. |
176 | * Can be called while holding spinlocks. |
177 | * |
178 | */ |
179 | static void get_futex_key_refs(union futex_key *key) |
180 | { |
181 | if (!key->both.ptr) |
182 | return; |
183 | |
184 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { |
185 | case FUT_OFF_INODE: |
186 | ihold(key->shared.inode); |
187 | break; |
188 | case FUT_OFF_MMSHARED: |
189 | atomic_inc(&key->private.mm->mm_count); |
190 | break; |
191 | } |
192 | } |
193 | |
194 | /* |
195 | * Drop a reference to the resource addressed by a key. |
196 | * The hash bucket spinlock must not be held. |
197 | */ |
198 | static void drop_futex_key_refs(union futex_key *key) |
199 | { |
200 | if (!key->both.ptr) { |
201 | /* If we're here then we tried to put a key we failed to get */ |
202 | WARN_ON_ONCE(1); |
203 | return; |
204 | } |
205 | |
206 | switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) { |
207 | case FUT_OFF_INODE: |
208 | iput(key->shared.inode); |
209 | break; |
210 | case FUT_OFF_MMSHARED: |
211 | mmdrop(key->private.mm); |
212 | break; |
213 | } |
214 | } |
215 | |
216 | /** |
217 | * get_futex_key() - Get parameters which are the keys for a futex |
218 | * @uaddr: virtual address of the futex |
219 | * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED |
220 | * @key: address where result is stored. |
221 | * @rw: mapping needs to be read/write (values: VERIFY_READ, |
222 | * VERIFY_WRITE) |
223 | * |
224 | * Returns a negative error code or 0 |
225 | * The key words are stored in *key on success. |
226 | * |
227 | * For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode, |
228 | * offset_within_page). For private mappings, it's (uaddr, current->mm). |
229 | * We can usually work out the index without swapping in the page. |
230 | * |
231 | * lock_page() might sleep, the caller should not hold a spinlock. |
232 | */ |
233 | static int |
234 | get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw) |
235 | { |
236 | unsigned long address = (unsigned long)uaddr; |
237 | struct mm_struct *mm = current->mm; |
238 | struct page *page, *page_head; |
239 | int err, ro = 0; |
240 | |
241 | /* |
242 | * The futex address must be "naturally" aligned. |
243 | */ |
244 | key->both.offset = address % PAGE_SIZE; |
245 | if (unlikely((address % sizeof(u32)) != 0)) |
246 | return -EINVAL; |
247 | address -= key->both.offset; |
248 | |
249 | /* |
250 | * PROCESS_PRIVATE futexes are fast. |
251 | * As the mm cannot disappear under us and the 'key' only needs |
252 | * virtual address, we dont even have to find the underlying vma. |
253 | * Note : We do have to check 'uaddr' is a valid user address, |
254 | * but access_ok() should be faster than find_vma() |
255 | */ |
256 | if (!fshared) { |
257 | if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))) |
258 | return -EFAULT; |
259 | key->private.mm = mm; |
260 | key->private.address = address; |
261 | get_futex_key_refs(key); |
262 | return 0; |
263 | } |
264 | |
265 | again: |
266 | err = get_user_pages_fast(address, 1, 1, &page); |
267 | /* |
268 | * If write access is not required (eg. FUTEX_WAIT), try |
269 | * and get read-only access. |
270 | */ |
271 | if (err == -EFAULT && rw == VERIFY_READ) { |
272 | err = get_user_pages_fast(address, 1, 0, &page); |
273 | ro = 1; |
274 | } |
275 | if (err < 0) |
276 | return err; |
277 | else |
278 | err = 0; |
279 | |
280 | #ifdef CONFIG_TRANSPARENT_HUGEPAGE |
281 | page_head = page; |
282 | if (unlikely(PageTail(page))) { |
283 | put_page(page); |
284 | /* serialize against __split_huge_page_splitting() */ |
285 | local_irq_disable(); |
286 | if (likely(__get_user_pages_fast(address, 1, 1, &page) == 1)) { |
287 | page_head = compound_head(page); |
288 | /* |
289 | * page_head is valid pointer but we must pin |
290 | * it before taking the PG_lock and/or |
291 | * PG_compound_lock. The moment we re-enable |
292 | * irqs __split_huge_page_splitting() can |
293 | * return and the head page can be freed from |
294 | * under us. We can't take the PG_lock and/or |
295 | * PG_compound_lock on a page that could be |
296 | * freed from under us. |
297 | */ |
298 | if (page != page_head) { |
299 | get_page(page_head); |
300 | put_page(page); |
301 | } |
302 | local_irq_enable(); |
303 | } else { |
304 | local_irq_enable(); |
305 | goto again; |
306 | } |
307 | } |
308 | #else |
309 | page_head = compound_head(page); |
310 | if (page != page_head) { |
311 | get_page(page_head); |
312 | put_page(page); |
313 | } |
314 | #endif |
315 | |
316 | lock_page(page_head); |
317 | |
318 | /* |
319 | * If page_head->mapping is NULL, then it cannot be a PageAnon |
320 | * page; but it might be the ZERO_PAGE or in the gate area or |
321 | * in a special mapping (all cases which we are happy to fail); |
322 | * or it may have been a good file page when get_user_pages_fast |
323 | * found it, but truncated or holepunched or subjected to |
324 | * invalidate_complete_page2 before we got the page lock (also |
325 | * cases which we are happy to fail). And we hold a reference, |
326 | * so refcount care in invalidate_complete_page's remove_mapping |
327 | * prevents drop_caches from setting mapping to NULL beneath us. |
328 | * |
329 | * The case we do have to guard against is when memory pressure made |
330 | * shmem_writepage move it from filecache to swapcache beneath us: |
331 | * an unlikely race, but we do need to retry for page_head->mapping. |
332 | */ |
333 | if (!page_head->mapping) { |
334 | int shmem_swizzled = PageSwapCache(page_head); |
335 | unlock_page(page_head); |
336 | put_page(page_head); |
337 | if (shmem_swizzled) |
338 | goto again; |
339 | return -EFAULT; |
340 | } |
341 | |
342 | /* |
343 | * Private mappings are handled in a simple way. |
344 | * |
345 | * NOTE: When userspace waits on a MAP_SHARED mapping, even if |
346 | * it's a read-only handle, it's expected that futexes attach to |
347 | * the object not the particular process. |
348 | */ |
349 | if (PageAnon(page_head)) { |
350 | /* |
351 | * A RO anonymous page will never change and thus doesn't make |
352 | * sense for futex operations. |
353 | */ |
354 | if (ro) { |
355 | err = -EFAULT; |
356 | goto out; |
357 | } |
358 | |
359 | key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */ |
360 | key->private.mm = mm; |
361 | key->private.address = address; |
362 | } else { |
363 | key->both.offset |= FUT_OFF_INODE; /* inode-based key */ |
364 | key->shared.inode = page_head->mapping->host; |
365 | key->shared.pgoff = page_head->index; |
366 | } |
367 | |
368 | get_futex_key_refs(key); |
369 | |
370 | out: |
371 | unlock_page(page_head); |
372 | put_page(page_head); |
373 | return err; |
374 | } |
375 | |
376 | static inline void put_futex_key(union futex_key *key) |
377 | { |
378 | drop_futex_key_refs(key); |
379 | } |
380 | |
381 | /** |
382 | * fault_in_user_writeable() - Fault in user address and verify RW access |
383 | * @uaddr: pointer to faulting user space address |
384 | * |
385 | * Slow path to fixup the fault we just took in the atomic write |
386 | * access to @uaddr. |
387 | * |
388 | * We have no generic implementation of a non-destructive write to the |
389 | * user address. We know that we faulted in the atomic pagefault |
390 | * disabled section so we can as well avoid the #PF overhead by |
391 | * calling get_user_pages() right away. |
392 | */ |
393 | static int fault_in_user_writeable(u32 __user *uaddr) |
394 | { |
395 | struct mm_struct *mm = current->mm; |
396 | int ret; |
397 | |
398 | down_read(&mm->mmap_sem); |
399 | ret = fixup_user_fault(current, mm, (unsigned long)uaddr, |
400 | FAULT_FLAG_WRITE); |
401 | up_read(&mm->mmap_sem); |
402 | |
403 | return ret < 0 ? ret : 0; |
404 | } |
405 | |
406 | /** |
407 | * futex_top_waiter() - Return the highest priority waiter on a futex |
408 | * @hb: the hash bucket the futex_q's reside in |
409 | * @key: the futex key (to distinguish it from other futex futex_q's) |
410 | * |
411 | * Must be called with the hb lock held. |
412 | */ |
413 | static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb, |
414 | union futex_key *key) |
415 | { |
416 | struct futex_q *this; |
417 | |
418 | plist_for_each_entry(this, &hb->chain, list) { |
419 | if (match_futex(&this->key, key)) |
420 | return this; |
421 | } |
422 | return NULL; |
423 | } |
424 | |
425 | static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr, |
426 | u32 uval, u32 newval) |
427 | { |
428 | int ret; |
429 | |
430 | pagefault_disable(); |
431 | ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); |
432 | pagefault_enable(); |
433 | |
434 | return ret; |
435 | } |
436 | |
437 | static int get_futex_value_locked(u32 *dest, u32 __user *from) |
438 | { |
439 | int ret; |
440 | |
441 | pagefault_disable(); |
442 | ret = __copy_from_user_inatomic(dest, from, sizeof(u32)); |
443 | pagefault_enable(); |
444 | |
445 | return ret ? -EFAULT : 0; |
446 | } |
447 | |
448 | |
449 | /* |
450 | * PI code: |
451 | */ |
452 | static int refill_pi_state_cache(void) |
453 | { |
454 | struct futex_pi_state *pi_state; |
455 | |
456 | if (likely(current->pi_state_cache)) |
457 | return 0; |
458 | |
459 | pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL); |
460 | |
461 | if (!pi_state) |
462 | return -ENOMEM; |
463 | |
464 | INIT_LIST_HEAD(&pi_state->list); |
465 | /* pi_mutex gets initialized later */ |
466 | pi_state->owner = NULL; |
467 | atomic_set(&pi_state->refcount, 1); |
468 | pi_state->key = FUTEX_KEY_INIT; |
469 | |
470 | current->pi_state_cache = pi_state; |
471 | |
472 | return 0; |
473 | } |
474 | |
475 | static struct futex_pi_state * alloc_pi_state(void) |
476 | { |
477 | struct futex_pi_state *pi_state = current->pi_state_cache; |
478 | |
479 | WARN_ON(!pi_state); |
480 | current->pi_state_cache = NULL; |
481 | |
482 | return pi_state; |
483 | } |
484 | |
485 | static void free_pi_state(struct futex_pi_state *pi_state) |
486 | { |
487 | if (!atomic_dec_and_test(&pi_state->refcount)) |
488 | return; |
489 | |
490 | /* |
491 | * If pi_state->owner is NULL, the owner is most probably dying |
492 | * and has cleaned up the pi_state already |
493 | */ |
494 | if (pi_state->owner) { |
495 | raw_spin_lock_irq(&pi_state->owner->pi_lock); |
496 | list_del_init(&pi_state->list); |
497 | raw_spin_unlock_irq(&pi_state->owner->pi_lock); |
498 | |
499 | rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner); |
500 | } |
501 | |
502 | if (current->pi_state_cache) |
503 | kfree(pi_state); |
504 | else { |
505 | /* |
506 | * pi_state->list is already empty. |
507 | * clear pi_state->owner. |
508 | * refcount is at 0 - put it back to 1. |
509 | */ |
510 | pi_state->owner = NULL; |
511 | atomic_set(&pi_state->refcount, 1); |
512 | current->pi_state_cache = pi_state; |
513 | } |
514 | } |
515 | |
516 | /* |
517 | * Look up the task based on what TID userspace gave us. |
518 | * We dont trust it. |
519 | */ |
520 | static struct task_struct * futex_find_get_task(pid_t pid) |
521 | { |
522 | struct task_struct *p; |
523 | |
524 | rcu_read_lock(); |
525 | p = find_task_by_vpid(pid); |
526 | if (p) |
527 | get_task_struct(p); |
528 | |
529 | rcu_read_unlock(); |
530 | |
531 | return p; |
532 | } |
533 | |
534 | /* |
535 | * This task is holding PI mutexes at exit time => bad. |
536 | * Kernel cleans up PI-state, but userspace is likely hosed. |
537 | * (Robust-futex cleanup is separate and might save the day for userspace.) |
538 | */ |
539 | void exit_pi_state_list(struct task_struct *curr) |
540 | { |
541 | struct list_head *next, *head = &curr->pi_state_list; |
542 | struct futex_pi_state *pi_state; |
543 | struct futex_hash_bucket *hb; |
544 | union futex_key key = FUTEX_KEY_INIT; |
545 | |
546 | if (!futex_cmpxchg_enabled) |
547 | return; |
548 | /* |
549 | * We are a ZOMBIE and nobody can enqueue itself on |
550 | * pi_state_list anymore, but we have to be careful |
551 | * versus waiters unqueueing themselves: |
552 | */ |
553 | raw_spin_lock_irq(&curr->pi_lock); |
554 | while (!list_empty(head)) { |
555 | |
556 | next = head->next; |
557 | pi_state = list_entry(next, struct futex_pi_state, list); |
558 | key = pi_state->key; |
559 | hb = hash_futex(&key); |
560 | raw_spin_unlock_irq(&curr->pi_lock); |
561 | |
562 | spin_lock(&hb->lock); |
563 | |
564 | raw_spin_lock_irq(&curr->pi_lock); |
565 | /* |
566 | * We dropped the pi-lock, so re-check whether this |
567 | * task still owns the PI-state: |
568 | */ |
569 | if (head->next != next) { |
570 | spin_unlock(&hb->lock); |
571 | continue; |
572 | } |
573 | |
574 | WARN_ON(pi_state->owner != curr); |
575 | WARN_ON(list_empty(&pi_state->list)); |
576 | list_del_init(&pi_state->list); |
577 | pi_state->owner = NULL; |
578 | raw_spin_unlock_irq(&curr->pi_lock); |
579 | |
580 | rt_mutex_unlock(&pi_state->pi_mutex); |
581 | |
582 | spin_unlock(&hb->lock); |
583 | |
584 | raw_spin_lock_irq(&curr->pi_lock); |
585 | } |
586 | raw_spin_unlock_irq(&curr->pi_lock); |
587 | } |
588 | |
589 | static int |
590 | lookup_pi_state(u32 uval, struct futex_hash_bucket *hb, |
591 | union futex_key *key, struct futex_pi_state **ps) |
592 | { |
593 | struct futex_pi_state *pi_state = NULL; |
594 | struct futex_q *this, *next; |
595 | struct plist_head *head; |
596 | struct task_struct *p; |
597 | pid_t pid = uval & FUTEX_TID_MASK; |
598 | |
599 | head = &hb->chain; |
600 | |
601 | plist_for_each_entry_safe(this, next, head, list) { |
602 | if (match_futex(&this->key, key)) { |
603 | /* |
604 | * Another waiter already exists - bump up |
605 | * the refcount and return its pi_state: |
606 | */ |
607 | pi_state = this->pi_state; |
608 | /* |
609 | * Userspace might have messed up non-PI and PI futexes |
610 | */ |
611 | if (unlikely(!pi_state)) |
612 | return -EINVAL; |
613 | |
614 | WARN_ON(!atomic_read(&pi_state->refcount)); |
615 | |
616 | /* |
617 | * When pi_state->owner is NULL then the owner died |
618 | * and another waiter is on the fly. pi_state->owner |
619 | * is fixed up by the task which acquires |
620 | * pi_state->rt_mutex. |
621 | * |
622 | * We do not check for pid == 0 which can happen when |
623 | * the owner died and robust_list_exit() cleared the |
624 | * TID. |
625 | */ |
626 | if (pid && pi_state->owner) { |
627 | /* |
628 | * Bail out if user space manipulated the |
629 | * futex value. |
630 | */ |
631 | if (pid != task_pid_vnr(pi_state->owner)) |
632 | return -EINVAL; |
633 | } |
634 | |
635 | atomic_inc(&pi_state->refcount); |
636 | *ps = pi_state; |
637 | |
638 | return 0; |
639 | } |
640 | } |
641 | |
642 | /* |
643 | * We are the first waiter - try to look up the real owner and attach |
644 | * the new pi_state to it, but bail out when TID = 0 |
645 | */ |
646 | if (!pid) |
647 | return -ESRCH; |
648 | p = futex_find_get_task(pid); |
649 | if (!p) |
650 | return -ESRCH; |
651 | |
652 | /* |
653 | * We need to look at the task state flags to figure out, |
654 | * whether the task is exiting. To protect against the do_exit |
655 | * change of the task flags, we do this protected by |
656 | * p->pi_lock: |
657 | */ |
658 | raw_spin_lock_irq(&p->pi_lock); |
659 | if (unlikely(p->flags & PF_EXITING)) { |
660 | /* |
661 | * The task is on the way out. When PF_EXITPIDONE is |
662 | * set, we know that the task has finished the |
663 | * cleanup: |
664 | */ |
665 | int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN; |
666 | |
667 | raw_spin_unlock_irq(&p->pi_lock); |
668 | put_task_struct(p); |
669 | return ret; |
670 | } |
671 | |
672 | pi_state = alloc_pi_state(); |
673 | |
674 | /* |
675 | * Initialize the pi_mutex in locked state and make 'p' |
676 | * the owner of it: |
677 | */ |
678 | rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p); |
679 | |
680 | /* Store the key for possible exit cleanups: */ |
681 | pi_state->key = *key; |
682 | |
683 | WARN_ON(!list_empty(&pi_state->list)); |
684 | list_add(&pi_state->list, &p->pi_state_list); |
685 | pi_state->owner = p; |
686 | raw_spin_unlock_irq(&p->pi_lock); |
687 | |
688 | put_task_struct(p); |
689 | |
690 | *ps = pi_state; |
691 | |
692 | return 0; |
693 | } |
694 | |
695 | /** |
696 | * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex |
697 | * @uaddr: the pi futex user address |
698 | * @hb: the pi futex hash bucket |
699 | * @key: the futex key associated with uaddr and hb |
700 | * @ps: the pi_state pointer where we store the result of the |
701 | * lookup |
702 | * @task: the task to perform the atomic lock work for. This will |
703 | * be "current" except in the case of requeue pi. |
704 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) |
705 | * |
706 | * Returns: |
707 | * 0 - ready to wait |
708 | * 1 - acquired the lock |
709 | * <0 - error |
710 | * |
711 | * The hb->lock and futex_key refs shall be held by the caller. |
712 | */ |
713 | static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, |
714 | union futex_key *key, |
715 | struct futex_pi_state **ps, |
716 | struct task_struct *task, int set_waiters) |
717 | { |
718 | int lock_taken, ret, ownerdied = 0; |
719 | u32 uval, newval, curval, vpid = task_pid_vnr(task); |
720 | |
721 | retry: |
722 | ret = lock_taken = 0; |
723 | |
724 | /* |
725 | * To avoid races, we attempt to take the lock here again |
726 | * (by doing a 0 -> TID atomic cmpxchg), while holding all |
727 | * the locks. It will most likely not succeed. |
728 | */ |
729 | newval = vpid; |
730 | if (set_waiters) |
731 | newval |= FUTEX_WAITERS; |
732 | |
733 | if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval))) |
734 | return -EFAULT; |
735 | |
736 | /* |
737 | * Detect deadlocks. |
738 | */ |
739 | if ((unlikely((curval & FUTEX_TID_MASK) == vpid))) |
740 | return -EDEADLK; |
741 | |
742 | /* |
743 | * Surprise - we got the lock. Just return to userspace: |
744 | */ |
745 | if (unlikely(!curval)) |
746 | return 1; |
747 | |
748 | uval = curval; |
749 | |
750 | /* |
751 | * Set the FUTEX_WAITERS flag, so the owner will know it has someone |
752 | * to wake at the next unlock. |
753 | */ |
754 | newval = curval | FUTEX_WAITERS; |
755 | |
756 | /* |
757 | * There are two cases, where a futex might have no owner (the |
758 | * owner TID is 0): OWNER_DIED. We take over the futex in this |
759 | * case. We also do an unconditional take over, when the owner |
760 | * of the futex died. |
761 | * |
762 | * This is safe as we are protected by the hash bucket lock ! |
763 | */ |
764 | if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) { |
765 | /* Keep the OWNER_DIED bit */ |
766 | newval = (curval & ~FUTEX_TID_MASK) | vpid; |
767 | ownerdied = 0; |
768 | lock_taken = 1; |
769 | } |
770 | |
771 | if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))) |
772 | return -EFAULT; |
773 | if (unlikely(curval != uval)) |
774 | goto retry; |
775 | |
776 | /* |
777 | * We took the lock due to owner died take over. |
778 | */ |
779 | if (unlikely(lock_taken)) |
780 | return 1; |
781 | |
782 | /* |
783 | * We dont have the lock. Look up the PI state (or create it if |
784 | * we are the first waiter): |
785 | */ |
786 | ret = lookup_pi_state(uval, hb, key, ps); |
787 | |
788 | if (unlikely(ret)) { |
789 | switch (ret) { |
790 | case -ESRCH: |
791 | /* |
792 | * No owner found for this futex. Check if the |
793 | * OWNER_DIED bit is set to figure out whether |
794 | * this is a robust futex or not. |
795 | */ |
796 | if (get_futex_value_locked(&curval, uaddr)) |
797 | return -EFAULT; |
798 | |
799 | /* |
800 | * We simply start over in case of a robust |
801 | * futex. The code above will take the futex |
802 | * and return happy. |
803 | */ |
804 | if (curval & FUTEX_OWNER_DIED) { |
805 | ownerdied = 1; |
806 | goto retry; |
807 | } |
808 | default: |
809 | break; |
810 | } |
811 | } |
812 | |
813 | return ret; |
814 | } |
815 | |
816 | /** |
817 | * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket |
818 | * @q: The futex_q to unqueue |
819 | * |
820 | * The q->lock_ptr must not be NULL and must be held by the caller. |
821 | */ |
822 | static void __unqueue_futex(struct futex_q *q) |
823 | { |
824 | struct futex_hash_bucket *hb; |
825 | |
826 | if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr)) |
827 | || WARN_ON(plist_node_empty(&q->list))) |
828 | return; |
829 | |
830 | hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock); |
831 | plist_del(&q->list, &hb->chain); |
832 | } |
833 | |
834 | /* |
835 | * The hash bucket lock must be held when this is called. |
836 | * Afterwards, the futex_q must not be accessed. |
837 | */ |
838 | static void wake_futex(struct futex_q *q) |
839 | { |
840 | struct task_struct *p = q->task; |
841 | |
842 | /* |
843 | * We set q->lock_ptr = NULL _before_ we wake up the task. If |
844 | * a non-futex wake up happens on another CPU then the task |
845 | * might exit and p would dereference a non-existing task |
846 | * struct. Prevent this by holding a reference on p across the |
847 | * wake up. |
848 | */ |
849 | get_task_struct(p); |
850 | |
851 | __unqueue_futex(q); |
852 | /* |
853 | * The waiting task can free the futex_q as soon as |
854 | * q->lock_ptr = NULL is written, without taking any locks. A |
855 | * memory barrier is required here to prevent the following |
856 | * store to lock_ptr from getting ahead of the plist_del. |
857 | */ |
858 | smp_wmb(); |
859 | q->lock_ptr = NULL; |
860 | |
861 | wake_up_state(p, TASK_NORMAL); |
862 | put_task_struct(p); |
863 | } |
864 | |
865 | static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this) |
866 | { |
867 | struct task_struct *new_owner; |
868 | struct futex_pi_state *pi_state = this->pi_state; |
869 | u32 uninitialized_var(curval), newval; |
870 | |
871 | if (!pi_state) |
872 | return -EINVAL; |
873 | |
874 | /* |
875 | * If current does not own the pi_state then the futex is |
876 | * inconsistent and user space fiddled with the futex value. |
877 | */ |
878 | if (pi_state->owner != current) |
879 | return -EINVAL; |
880 | |
881 | raw_spin_lock(&pi_state->pi_mutex.wait_lock); |
882 | new_owner = rt_mutex_next_owner(&pi_state->pi_mutex); |
883 | |
884 | /* |
885 | * It is possible that the next waiter (the one that brought |
886 | * this owner to the kernel) timed out and is no longer |
887 | * waiting on the lock. |
888 | */ |
889 | if (!new_owner) |
890 | new_owner = this->task; |
891 | |
892 | /* |
893 | * We pass it to the next owner. (The WAITERS bit is always |
894 | * kept enabled while there is PI state around. We must also |
895 | * preserve the owner died bit.) |
896 | */ |
897 | if (!(uval & FUTEX_OWNER_DIED)) { |
898 | int ret = 0; |
899 | |
900 | newval = FUTEX_WAITERS | task_pid_vnr(new_owner); |
901 | |
902 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) |
903 | ret = -EFAULT; |
904 | else if (curval != uval) |
905 | ret = -EINVAL; |
906 | if (ret) { |
907 | raw_spin_unlock(&pi_state->pi_mutex.wait_lock); |
908 | return ret; |
909 | } |
910 | } |
911 | |
912 | raw_spin_lock_irq(&pi_state->owner->pi_lock); |
913 | WARN_ON(list_empty(&pi_state->list)); |
914 | list_del_init(&pi_state->list); |
915 | raw_spin_unlock_irq(&pi_state->owner->pi_lock); |
916 | |
917 | raw_spin_lock_irq(&new_owner->pi_lock); |
918 | WARN_ON(!list_empty(&pi_state->list)); |
919 | list_add(&pi_state->list, &new_owner->pi_state_list); |
920 | pi_state->owner = new_owner; |
921 | raw_spin_unlock_irq(&new_owner->pi_lock); |
922 | |
923 | raw_spin_unlock(&pi_state->pi_mutex.wait_lock); |
924 | rt_mutex_unlock(&pi_state->pi_mutex); |
925 | |
926 | return 0; |
927 | } |
928 | |
929 | static int unlock_futex_pi(u32 __user *uaddr, u32 uval) |
930 | { |
931 | u32 uninitialized_var(oldval); |
932 | |
933 | /* |
934 | * There is no waiter, so we unlock the futex. The owner died |
935 | * bit has not to be preserved here. We are the owner: |
936 | */ |
937 | if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0)) |
938 | return -EFAULT; |
939 | if (oldval != uval) |
940 | return -EAGAIN; |
941 | |
942 | return 0; |
943 | } |
944 | |
945 | /* |
946 | * Express the locking dependencies for lockdep: |
947 | */ |
948 | static inline void |
949 | double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) |
950 | { |
951 | if (hb1 <= hb2) { |
952 | spin_lock(&hb1->lock); |
953 | if (hb1 < hb2) |
954 | spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); |
955 | } else { /* hb1 > hb2 */ |
956 | spin_lock(&hb2->lock); |
957 | spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); |
958 | } |
959 | } |
960 | |
961 | static inline void |
962 | double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) |
963 | { |
964 | spin_unlock(&hb1->lock); |
965 | if (hb1 != hb2) |
966 | spin_unlock(&hb2->lock); |
967 | } |
968 | |
969 | /* |
970 | * Wake up waiters matching bitset queued on this futex (uaddr). |
971 | */ |
972 | static int |
973 | futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) |
974 | { |
975 | struct futex_hash_bucket *hb; |
976 | struct futex_q *this, *next; |
977 | struct plist_head *head; |
978 | union futex_key key = FUTEX_KEY_INIT; |
979 | int ret; |
980 | |
981 | if (!bitset) |
982 | return -EINVAL; |
983 | |
984 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ); |
985 | if (unlikely(ret != 0)) |
986 | goto out; |
987 | |
988 | hb = hash_futex(&key); |
989 | spin_lock(&hb->lock); |
990 | head = &hb->chain; |
991 | |
992 | plist_for_each_entry_safe(this, next, head, list) { |
993 | if (match_futex (&this->key, &key)) { |
994 | if (this->pi_state || this->rt_waiter) { |
995 | ret = -EINVAL; |
996 | break; |
997 | } |
998 | |
999 | /* Check if one of the bits is set in both bitsets */ |
1000 | if (!(this->bitset & bitset)) |
1001 | continue; |
1002 | |
1003 | wake_futex(this); |
1004 | if (++ret >= nr_wake) |
1005 | break; |
1006 | } |
1007 | } |
1008 | |
1009 | spin_unlock(&hb->lock); |
1010 | put_futex_key(&key); |
1011 | out: |
1012 | return ret; |
1013 | } |
1014 | |
1015 | /* |
1016 | * Wake up all waiters hashed on the physical page that is mapped |
1017 | * to this virtual address: |
1018 | */ |
1019 | static int |
1020 | futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, |
1021 | int nr_wake, int nr_wake2, int op) |
1022 | { |
1023 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; |
1024 | struct futex_hash_bucket *hb1, *hb2; |
1025 | struct plist_head *head; |
1026 | struct futex_q *this, *next; |
1027 | int ret, op_ret; |
1028 | |
1029 | retry: |
1030 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); |
1031 | if (unlikely(ret != 0)) |
1032 | goto out; |
1033 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE); |
1034 | if (unlikely(ret != 0)) |
1035 | goto out_put_key1; |
1036 | |
1037 | hb1 = hash_futex(&key1); |
1038 | hb2 = hash_futex(&key2); |
1039 | |
1040 | retry_private: |
1041 | double_lock_hb(hb1, hb2); |
1042 | op_ret = futex_atomic_op_inuser(op, uaddr2); |
1043 | if (unlikely(op_ret < 0)) { |
1044 | |
1045 | double_unlock_hb(hb1, hb2); |
1046 | |
1047 | #ifndef CONFIG_MMU |
1048 | /* |
1049 | * we don't get EFAULT from MMU faults if we don't have an MMU, |
1050 | * but we might get them from range checking |
1051 | */ |
1052 | ret = op_ret; |
1053 | goto out_put_keys; |
1054 | #endif |
1055 | |
1056 | if (unlikely(op_ret != -EFAULT)) { |
1057 | ret = op_ret; |
1058 | goto out_put_keys; |
1059 | } |
1060 | |
1061 | ret = fault_in_user_writeable(uaddr2); |
1062 | if (ret) |
1063 | goto out_put_keys; |
1064 | |
1065 | if (!(flags & FLAGS_SHARED)) |
1066 | goto retry_private; |
1067 | |
1068 | put_futex_key(&key2); |
1069 | put_futex_key(&key1); |
1070 | goto retry; |
1071 | } |
1072 | |
1073 | head = &hb1->chain; |
1074 | |
1075 | plist_for_each_entry_safe(this, next, head, list) { |
1076 | if (match_futex (&this->key, &key1)) { |
1077 | wake_futex(this); |
1078 | if (++ret >= nr_wake) |
1079 | break; |
1080 | } |
1081 | } |
1082 | |
1083 | if (op_ret > 0) { |
1084 | head = &hb2->chain; |
1085 | |
1086 | op_ret = 0; |
1087 | plist_for_each_entry_safe(this, next, head, list) { |
1088 | if (match_futex (&this->key, &key2)) { |
1089 | wake_futex(this); |
1090 | if (++op_ret >= nr_wake2) |
1091 | break; |
1092 | } |
1093 | } |
1094 | ret += op_ret; |
1095 | } |
1096 | |
1097 | double_unlock_hb(hb1, hb2); |
1098 | out_put_keys: |
1099 | put_futex_key(&key2); |
1100 | out_put_key1: |
1101 | put_futex_key(&key1); |
1102 | out: |
1103 | return ret; |
1104 | } |
1105 | |
1106 | /** |
1107 | * requeue_futex() - Requeue a futex_q from one hb to another |
1108 | * @q: the futex_q to requeue |
1109 | * @hb1: the source hash_bucket |
1110 | * @hb2: the target hash_bucket |
1111 | * @key2: the new key for the requeued futex_q |
1112 | */ |
1113 | static inline |
1114 | void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1, |
1115 | struct futex_hash_bucket *hb2, union futex_key *key2) |
1116 | { |
1117 | |
1118 | /* |
1119 | * If key1 and key2 hash to the same bucket, no need to |
1120 | * requeue. |
1121 | */ |
1122 | if (likely(&hb1->chain != &hb2->chain)) { |
1123 | plist_del(&q->list, &hb1->chain); |
1124 | plist_add(&q->list, &hb2->chain); |
1125 | q->lock_ptr = &hb2->lock; |
1126 | } |
1127 | get_futex_key_refs(key2); |
1128 | q->key = *key2; |
1129 | } |
1130 | |
1131 | /** |
1132 | * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue |
1133 | * @q: the futex_q |
1134 | * @key: the key of the requeue target futex |
1135 | * @hb: the hash_bucket of the requeue target futex |
1136 | * |
1137 | * During futex_requeue, with requeue_pi=1, it is possible to acquire the |
1138 | * target futex if it is uncontended or via a lock steal. Set the futex_q key |
1139 | * to the requeue target futex so the waiter can detect the wakeup on the right |
1140 | * futex, but remove it from the hb and NULL the rt_waiter so it can detect |
1141 | * atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock |
1142 | * to protect access to the pi_state to fixup the owner later. Must be called |
1143 | * with both q->lock_ptr and hb->lock held. |
1144 | */ |
1145 | static inline |
1146 | void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, |
1147 | struct futex_hash_bucket *hb) |
1148 | { |
1149 | get_futex_key_refs(key); |
1150 | q->key = *key; |
1151 | |
1152 | __unqueue_futex(q); |
1153 | |
1154 | WARN_ON(!q->rt_waiter); |
1155 | q->rt_waiter = NULL; |
1156 | |
1157 | q->lock_ptr = &hb->lock; |
1158 | |
1159 | wake_up_state(q->task, TASK_NORMAL); |
1160 | } |
1161 | |
1162 | /** |
1163 | * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter |
1164 | * @pifutex: the user address of the to futex |
1165 | * @hb1: the from futex hash bucket, must be locked by the caller |
1166 | * @hb2: the to futex hash bucket, must be locked by the caller |
1167 | * @key1: the from futex key |
1168 | * @key2: the to futex key |
1169 | * @ps: address to store the pi_state pointer |
1170 | * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0) |
1171 | * |
1172 | * Try and get the lock on behalf of the top waiter if we can do it atomically. |
1173 | * Wake the top waiter if we succeed. If the caller specified set_waiters, |
1174 | * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit. |
1175 | * hb1 and hb2 must be held by the caller. |
1176 | * |
1177 | * Returns: |
1178 | * 0 - failed to acquire the lock atomicly |
1179 | * 1 - acquired the lock |
1180 | * <0 - error |
1181 | */ |
1182 | static int futex_proxy_trylock_atomic(u32 __user *pifutex, |
1183 | struct futex_hash_bucket *hb1, |
1184 | struct futex_hash_bucket *hb2, |
1185 | union futex_key *key1, union futex_key *key2, |
1186 | struct futex_pi_state **ps, int set_waiters) |
1187 | { |
1188 | struct futex_q *top_waiter = NULL; |
1189 | u32 curval; |
1190 | int ret; |
1191 | |
1192 | if (get_futex_value_locked(&curval, pifutex)) |
1193 | return -EFAULT; |
1194 | |
1195 | /* |
1196 | * Find the top_waiter and determine if there are additional waiters. |
1197 | * If the caller intends to requeue more than 1 waiter to pifutex, |
1198 | * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now, |
1199 | * as we have means to handle the possible fault. If not, don't set |
1200 | * the bit unecessarily as it will force the subsequent unlock to enter |
1201 | * the kernel. |
1202 | */ |
1203 | top_waiter = futex_top_waiter(hb1, key1); |
1204 | |
1205 | /* There are no waiters, nothing for us to do. */ |
1206 | if (!top_waiter) |
1207 | return 0; |
1208 | |
1209 | /* Ensure we requeue to the expected futex. */ |
1210 | if (!match_futex(top_waiter->requeue_pi_key, key2)) |
1211 | return -EINVAL; |
1212 | |
1213 | /* |
1214 | * Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in |
1215 | * the contended case or if set_waiters is 1. The pi_state is returned |
1216 | * in ps in contended cases. |
1217 | */ |
1218 | ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task, |
1219 | set_waiters); |
1220 | if (ret == 1) |
1221 | requeue_pi_wake_futex(top_waiter, key2, hb2); |
1222 | |
1223 | return ret; |
1224 | } |
1225 | |
1226 | /** |
1227 | * futex_requeue() - Requeue waiters from uaddr1 to uaddr2 |
1228 | * @uaddr1: source futex user address |
1229 | * @flags: futex flags (FLAGS_SHARED, etc.) |
1230 | * @uaddr2: target futex user address |
1231 | * @nr_wake: number of waiters to wake (must be 1 for requeue_pi) |
1232 | * @nr_requeue: number of waiters to requeue (0-INT_MAX) |
1233 | * @cmpval: @uaddr1 expected value (or %NULL) |
1234 | * @requeue_pi: if we are attempting to requeue from a non-pi futex to a |
1235 | * pi futex (pi to pi requeue is not supported) |
1236 | * |
1237 | * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire |
1238 | * uaddr2 atomically on behalf of the top waiter. |
1239 | * |
1240 | * Returns: |
1241 | * >=0 - on success, the number of tasks requeued or woken |
1242 | * <0 - on error |
1243 | */ |
1244 | static int futex_requeue(u32 __user *uaddr1, unsigned int flags, |
1245 | u32 __user *uaddr2, int nr_wake, int nr_requeue, |
1246 | u32 *cmpval, int requeue_pi) |
1247 | { |
1248 | union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT; |
1249 | int drop_count = 0, task_count = 0, ret; |
1250 | struct futex_pi_state *pi_state = NULL; |
1251 | struct futex_hash_bucket *hb1, *hb2; |
1252 | struct plist_head *head1; |
1253 | struct futex_q *this, *next; |
1254 | u32 curval2; |
1255 | |
1256 | if (requeue_pi) { |
1257 | /* |
1258 | * requeue_pi requires a pi_state, try to allocate it now |
1259 | * without any locks in case it fails. |
1260 | */ |
1261 | if (refill_pi_state_cache()) |
1262 | return -ENOMEM; |
1263 | /* |
1264 | * requeue_pi must wake as many tasks as it can, up to nr_wake |
1265 | * + nr_requeue, since it acquires the rt_mutex prior to |
1266 | * returning to userspace, so as to not leave the rt_mutex with |
1267 | * waiters and no owner. However, second and third wake-ups |
1268 | * cannot be predicted as they involve race conditions with the |
1269 | * first wake and a fault while looking up the pi_state. Both |
1270 | * pthread_cond_signal() and pthread_cond_broadcast() should |
1271 | * use nr_wake=1. |
1272 | */ |
1273 | if (nr_wake != 1) |
1274 | return -EINVAL; |
1275 | } |
1276 | |
1277 | retry: |
1278 | if (pi_state != NULL) { |
1279 | /* |
1280 | * We will have to lookup the pi_state again, so free this one |
1281 | * to keep the accounting correct. |
1282 | */ |
1283 | free_pi_state(pi_state); |
1284 | pi_state = NULL; |
1285 | } |
1286 | |
1287 | ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); |
1288 | if (unlikely(ret != 0)) |
1289 | goto out; |
1290 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, |
1291 | requeue_pi ? VERIFY_WRITE : VERIFY_READ); |
1292 | if (unlikely(ret != 0)) |
1293 | goto out_put_key1; |
1294 | |
1295 | hb1 = hash_futex(&key1); |
1296 | hb2 = hash_futex(&key2); |
1297 | |
1298 | retry_private: |
1299 | double_lock_hb(hb1, hb2); |
1300 | |
1301 | if (likely(cmpval != NULL)) { |
1302 | u32 curval; |
1303 | |
1304 | ret = get_futex_value_locked(&curval, uaddr1); |
1305 | |
1306 | if (unlikely(ret)) { |
1307 | double_unlock_hb(hb1, hb2); |
1308 | |
1309 | ret = get_user(curval, uaddr1); |
1310 | if (ret) |
1311 | goto out_put_keys; |
1312 | |
1313 | if (!(flags & FLAGS_SHARED)) |
1314 | goto retry_private; |
1315 | |
1316 | put_futex_key(&key2); |
1317 | put_futex_key(&key1); |
1318 | goto retry; |
1319 | } |
1320 | if (curval != *cmpval) { |
1321 | ret = -EAGAIN; |
1322 | goto out_unlock; |
1323 | } |
1324 | } |
1325 | |
1326 | if (requeue_pi && (task_count - nr_wake < nr_requeue)) { |
1327 | /* |
1328 | * Attempt to acquire uaddr2 and wake the top waiter. If we |
1329 | * intend to requeue waiters, force setting the FUTEX_WAITERS |
1330 | * bit. We force this here where we are able to easily handle |
1331 | * faults rather in the requeue loop below. |
1332 | */ |
1333 | ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1, |
1334 | &key2, &pi_state, nr_requeue); |
1335 | |
1336 | /* |
1337 | * At this point the top_waiter has either taken uaddr2 or is |
1338 | * waiting on it. If the former, then the pi_state will not |
1339 | * exist yet, look it up one more time to ensure we have a |
1340 | * reference to it. |
1341 | */ |
1342 | if (ret == 1) { |
1343 | WARN_ON(pi_state); |
1344 | drop_count++; |
1345 | task_count++; |
1346 | ret = get_futex_value_locked(&curval2, uaddr2); |
1347 | if (!ret) |
1348 | ret = lookup_pi_state(curval2, hb2, &key2, |
1349 | &pi_state); |
1350 | } |
1351 | |
1352 | switch (ret) { |
1353 | case 0: |
1354 | break; |
1355 | case -EFAULT: |
1356 | double_unlock_hb(hb1, hb2); |
1357 | put_futex_key(&key2); |
1358 | put_futex_key(&key1); |
1359 | ret = fault_in_user_writeable(uaddr2); |
1360 | if (!ret) |
1361 | goto retry; |
1362 | goto out; |
1363 | case -EAGAIN: |
1364 | /* The owner was exiting, try again. */ |
1365 | double_unlock_hb(hb1, hb2); |
1366 | put_futex_key(&key2); |
1367 | put_futex_key(&key1); |
1368 | cond_resched(); |
1369 | goto retry; |
1370 | default: |
1371 | goto out_unlock; |
1372 | } |
1373 | } |
1374 | |
1375 | head1 = &hb1->chain; |
1376 | plist_for_each_entry_safe(this, next, head1, list) { |
1377 | if (task_count - nr_wake >= nr_requeue) |
1378 | break; |
1379 | |
1380 | if (!match_futex(&this->key, &key1)) |
1381 | continue; |
1382 | |
1383 | /* |
1384 | * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always |
1385 | * be paired with each other and no other futex ops. |
1386 | */ |
1387 | if ((requeue_pi && !this->rt_waiter) || |
1388 | (!requeue_pi && this->rt_waiter)) { |
1389 | ret = -EINVAL; |
1390 | break; |
1391 | } |
1392 | |
1393 | /* |
1394 | * Wake nr_wake waiters. For requeue_pi, if we acquired the |
1395 | * lock, we already woke the top_waiter. If not, it will be |
1396 | * woken by futex_unlock_pi(). |
1397 | */ |
1398 | if (++task_count <= nr_wake && !requeue_pi) { |
1399 | wake_futex(this); |
1400 | continue; |
1401 | } |
1402 | |
1403 | /* Ensure we requeue to the expected futex for requeue_pi. */ |
1404 | if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) { |
1405 | ret = -EINVAL; |
1406 | break; |
1407 | } |
1408 | |
1409 | /* |
1410 | * Requeue nr_requeue waiters and possibly one more in the case |
1411 | * of requeue_pi if we couldn't acquire the lock atomically. |
1412 | */ |
1413 | if (requeue_pi) { |
1414 | /* Prepare the waiter to take the rt_mutex. */ |
1415 | atomic_inc(&pi_state->refcount); |
1416 | this->pi_state = pi_state; |
1417 | ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex, |
1418 | this->rt_waiter, |
1419 | this->task, 1); |
1420 | if (ret == 1) { |
1421 | /* We got the lock. */ |
1422 | requeue_pi_wake_futex(this, &key2, hb2); |
1423 | drop_count++; |
1424 | continue; |
1425 | } else if (ret) { |
1426 | /* -EDEADLK */ |
1427 | this->pi_state = NULL; |
1428 | free_pi_state(pi_state); |
1429 | goto out_unlock; |
1430 | } |
1431 | } |
1432 | requeue_futex(this, hb1, hb2, &key2); |
1433 | drop_count++; |
1434 | } |
1435 | |
1436 | out_unlock: |
1437 | double_unlock_hb(hb1, hb2); |
1438 | |
1439 | /* |
1440 | * drop_futex_key_refs() must be called outside the spinlocks. During |
1441 | * the requeue we moved futex_q's from the hash bucket at key1 to the |
1442 | * one at key2 and updated their key pointer. We no longer need to |
1443 | * hold the references to key1. |
1444 | */ |
1445 | while (--drop_count >= 0) |
1446 | drop_futex_key_refs(&key1); |
1447 | |
1448 | out_put_keys: |
1449 | put_futex_key(&key2); |
1450 | out_put_key1: |
1451 | put_futex_key(&key1); |
1452 | out: |
1453 | if (pi_state != NULL) |
1454 | free_pi_state(pi_state); |
1455 | return ret ? ret : task_count; |
1456 | } |
1457 | |
1458 | /* The key must be already stored in q->key. */ |
1459 | static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) |
1460 | __acquires(&hb->lock) |
1461 | { |
1462 | struct futex_hash_bucket *hb; |
1463 | |
1464 | hb = hash_futex(&q->key); |
1465 | q->lock_ptr = &hb->lock; |
1466 | |
1467 | spin_lock(&hb->lock); |
1468 | return hb; |
1469 | } |
1470 | |
1471 | static inline void |
1472 | queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb) |
1473 | __releases(&hb->lock) |
1474 | { |
1475 | spin_unlock(&hb->lock); |
1476 | } |
1477 | |
1478 | /** |
1479 | * queue_me() - Enqueue the futex_q on the futex_hash_bucket |
1480 | * @q: The futex_q to enqueue |
1481 | * @hb: The destination hash bucket |
1482 | * |
1483 | * The hb->lock must be held by the caller, and is released here. A call to |
1484 | * queue_me() is typically paired with exactly one call to unqueue_me(). The |
1485 | * exceptions involve the PI related operations, which may use unqueue_me_pi() |
1486 | * or nothing if the unqueue is done as part of the wake process and the unqueue |
1487 | * state is implicit in the state of woken task (see futex_wait_requeue_pi() for |
1488 | * an example). |
1489 | */ |
1490 | static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) |
1491 | __releases(&hb->lock) |
1492 | { |
1493 | int prio; |
1494 | |
1495 | /* |
1496 | * The priority used to register this element is |
1497 | * - either the real thread-priority for the real-time threads |
1498 | * (i.e. threads with a priority lower than MAX_RT_PRIO) |
1499 | * - or MAX_RT_PRIO for non-RT threads. |
1500 | * Thus, all RT-threads are woken first in priority order, and |
1501 | * the others are woken last, in FIFO order. |
1502 | */ |
1503 | prio = min(current->normal_prio, MAX_RT_PRIO); |
1504 | |
1505 | plist_node_init(&q->list, prio); |
1506 | plist_add(&q->list, &hb->chain); |
1507 | q->task = current; |
1508 | spin_unlock(&hb->lock); |
1509 | } |
1510 | |
1511 | /** |
1512 | * unqueue_me() - Remove the futex_q from its futex_hash_bucket |
1513 | * @q: The futex_q to unqueue |
1514 | * |
1515 | * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must |
1516 | * be paired with exactly one earlier call to queue_me(). |
1517 | * |
1518 | * Returns: |
1519 | * 1 - if the futex_q was still queued (and we removed unqueued it) |
1520 | * 0 - if the futex_q was already removed by the waking thread |
1521 | */ |
1522 | static int unqueue_me(struct futex_q *q) |
1523 | { |
1524 | spinlock_t *lock_ptr; |
1525 | int ret = 0; |
1526 | |
1527 | /* In the common case we don't take the spinlock, which is nice. */ |
1528 | retry: |
1529 | lock_ptr = q->lock_ptr; |
1530 | barrier(); |
1531 | if (lock_ptr != NULL) { |
1532 | spin_lock(lock_ptr); |
1533 | /* |
1534 | * q->lock_ptr can change between reading it and |
1535 | * spin_lock(), causing us to take the wrong lock. This |
1536 | * corrects the race condition. |
1537 | * |
1538 | * Reasoning goes like this: if we have the wrong lock, |
1539 | * q->lock_ptr must have changed (maybe several times) |
1540 | * between reading it and the spin_lock(). It can |
1541 | * change again after the spin_lock() but only if it was |
1542 | * already changed before the spin_lock(). It cannot, |
1543 | * however, change back to the original value. Therefore |
1544 | * we can detect whether we acquired the correct lock. |
1545 | */ |
1546 | if (unlikely(lock_ptr != q->lock_ptr)) { |
1547 | spin_unlock(lock_ptr); |
1548 | goto retry; |
1549 | } |
1550 | __unqueue_futex(q); |
1551 | |
1552 | BUG_ON(q->pi_state); |
1553 | |
1554 | spin_unlock(lock_ptr); |
1555 | ret = 1; |
1556 | } |
1557 | |
1558 | drop_futex_key_refs(&q->key); |
1559 | return ret; |
1560 | } |
1561 | |
1562 | /* |
1563 | * PI futexes can not be requeued and must remove themself from the |
1564 | * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry |
1565 | * and dropped here. |
1566 | */ |
1567 | static void unqueue_me_pi(struct futex_q *q) |
1568 | __releases(q->lock_ptr) |
1569 | { |
1570 | __unqueue_futex(q); |
1571 | |
1572 | BUG_ON(!q->pi_state); |
1573 | free_pi_state(q->pi_state); |
1574 | q->pi_state = NULL; |
1575 | |
1576 | spin_unlock(q->lock_ptr); |
1577 | } |
1578 | |
1579 | /* |
1580 | * Fixup the pi_state owner with the new owner. |
1581 | * |
1582 | * Must be called with hash bucket lock held and mm->sem held for non |
1583 | * private futexes. |
1584 | */ |
1585 | static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, |
1586 | struct task_struct *newowner) |
1587 | { |
1588 | u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS; |
1589 | struct futex_pi_state *pi_state = q->pi_state; |
1590 | struct task_struct *oldowner = pi_state->owner; |
1591 | u32 uval, uninitialized_var(curval), newval; |
1592 | int ret; |
1593 | |
1594 | /* Owner died? */ |
1595 | if (!pi_state->owner) |
1596 | newtid |= FUTEX_OWNER_DIED; |
1597 | |
1598 | /* |
1599 | * We are here either because we stole the rtmutex from the |
1600 | * previous highest priority waiter or we are the highest priority |
1601 | * waiter but failed to get the rtmutex the first time. |
1602 | * We have to replace the newowner TID in the user space variable. |
1603 | * This must be atomic as we have to preserve the owner died bit here. |
1604 | * |
1605 | * Note: We write the user space value _before_ changing the pi_state |
1606 | * because we can fault here. Imagine swapped out pages or a fork |
1607 | * that marked all the anonymous memory readonly for cow. |
1608 | * |
1609 | * Modifying pi_state _before_ the user space value would |
1610 | * leave the pi_state in an inconsistent state when we fault |
1611 | * here, because we need to drop the hash bucket lock to |
1612 | * handle the fault. This might be observed in the PID check |
1613 | * in lookup_pi_state. |
1614 | */ |
1615 | retry: |
1616 | if (get_futex_value_locked(&uval, uaddr)) |
1617 | goto handle_fault; |
1618 | |
1619 | while (1) { |
1620 | newval = (uval & FUTEX_OWNER_DIED) | newtid; |
1621 | |
1622 | if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) |
1623 | goto handle_fault; |
1624 | if (curval == uval) |
1625 | break; |
1626 | uval = curval; |
1627 | } |
1628 | |
1629 | /* |
1630 | * We fixed up user space. Now we need to fix the pi_state |
1631 | * itself. |
1632 | */ |
1633 | if (pi_state->owner != NULL) { |
1634 | raw_spin_lock_irq(&pi_state->owner->pi_lock); |
1635 | WARN_ON(list_empty(&pi_state->list)); |
1636 | list_del_init(&pi_state->list); |
1637 | raw_spin_unlock_irq(&pi_state->owner->pi_lock); |
1638 | } |
1639 | |
1640 | pi_state->owner = newowner; |
1641 | |
1642 | raw_spin_lock_irq(&newowner->pi_lock); |
1643 | WARN_ON(!list_empty(&pi_state->list)); |
1644 | list_add(&pi_state->list, &newowner->pi_state_list); |
1645 | raw_spin_unlock_irq(&newowner->pi_lock); |
1646 | return 0; |
1647 | |
1648 | /* |
1649 | * To handle the page fault we need to drop the hash bucket |
1650 | * lock here. That gives the other task (either the highest priority |
1651 | * waiter itself or the task which stole the rtmutex) the |
1652 | * chance to try the fixup of the pi_state. So once we are |
1653 | * back from handling the fault we need to check the pi_state |
1654 | * after reacquiring the hash bucket lock and before trying to |
1655 | * do another fixup. When the fixup has been done already we |
1656 | * simply return. |
1657 | */ |
1658 | handle_fault: |
1659 | spin_unlock(q->lock_ptr); |
1660 | |
1661 | ret = fault_in_user_writeable(uaddr); |
1662 | |
1663 | spin_lock(q->lock_ptr); |
1664 | |
1665 | /* |
1666 | * Check if someone else fixed it for us: |
1667 | */ |
1668 | if (pi_state->owner != oldowner) |
1669 | return 0; |
1670 | |
1671 | if (ret) |
1672 | return ret; |
1673 | |
1674 | goto retry; |
1675 | } |
1676 | |
1677 | static long futex_wait_restart(struct restart_block *restart); |
1678 | |
1679 | /** |
1680 | * fixup_owner() - Post lock pi_state and corner case management |
1681 | * @uaddr: user address of the futex |
1682 | * @q: futex_q (contains pi_state and access to the rt_mutex) |
1683 | * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0) |
1684 | * |
1685 | * After attempting to lock an rt_mutex, this function is called to cleanup |
1686 | * the pi_state owner as well as handle race conditions that may allow us to |
1687 | * acquire the lock. Must be called with the hb lock held. |
1688 | * |
1689 | * Returns: |
1690 | * 1 - success, lock taken |
1691 | * 0 - success, lock not taken |
1692 | * <0 - on error (-EFAULT) |
1693 | */ |
1694 | static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked) |
1695 | { |
1696 | struct task_struct *owner; |
1697 | int ret = 0; |
1698 | |
1699 | if (locked) { |
1700 | /* |
1701 | * Got the lock. We might not be the anticipated owner if we |
1702 | * did a lock-steal - fix up the PI-state in that case: |
1703 | */ |
1704 | if (q->pi_state->owner != current) |
1705 | ret = fixup_pi_state_owner(uaddr, q, current); |
1706 | goto out; |
1707 | } |
1708 | |
1709 | /* |
1710 | * Catch the rare case, where the lock was released when we were on the |
1711 | * way back before we locked the hash bucket. |
1712 | */ |
1713 | if (q->pi_state->owner == current) { |
1714 | /* |
1715 | * Try to get the rt_mutex now. This might fail as some other |
1716 | * task acquired the rt_mutex after we removed ourself from the |
1717 | * rt_mutex waiters list. |
1718 | */ |
1719 | if (rt_mutex_trylock(&q->pi_state->pi_mutex)) { |
1720 | locked = 1; |
1721 | goto out; |
1722 | } |
1723 | |
1724 | /* |
1725 | * pi_state is incorrect, some other task did a lock steal and |
1726 | * we returned due to timeout or signal without taking the |
1727 | * rt_mutex. Too late. |
1728 | */ |
1729 | raw_spin_lock(&q->pi_state->pi_mutex.wait_lock); |
1730 | owner = rt_mutex_owner(&q->pi_state->pi_mutex); |
1731 | if (!owner) |
1732 | owner = rt_mutex_next_owner(&q->pi_state->pi_mutex); |
1733 | raw_spin_unlock(&q->pi_state->pi_mutex.wait_lock); |
1734 | ret = fixup_pi_state_owner(uaddr, q, owner); |
1735 | goto out; |
1736 | } |
1737 | |
1738 | /* |
1739 | * Paranoia check. If we did not take the lock, then we should not be |
1740 | * the owner of the rt_mutex. |
1741 | */ |
1742 | if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) |
1743 | printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p " |
1744 | "pi-state %p\n", ret, |
1745 | q->pi_state->pi_mutex.owner, |
1746 | q->pi_state->owner); |
1747 | |
1748 | out: |
1749 | return ret ? ret : locked; |
1750 | } |
1751 | |
1752 | /** |
1753 | * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal |
1754 | * @hb: the futex hash bucket, must be locked by the caller |
1755 | * @q: the futex_q to queue up on |
1756 | * @timeout: the prepared hrtimer_sleeper, or null for no timeout |
1757 | */ |
1758 | static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, |
1759 | struct hrtimer_sleeper *timeout) |
1760 | { |
1761 | /* |
1762 | * The task state is guaranteed to be set before another task can |
1763 | * wake it. set_current_state() is implemented using set_mb() and |
1764 | * queue_me() calls spin_unlock() upon completion, both serializing |
1765 | * access to the hash list and forcing another memory barrier. |
1766 | */ |
1767 | set_current_state(TASK_INTERRUPTIBLE); |
1768 | queue_me(q, hb); |
1769 | |
1770 | /* Arm the timer */ |
1771 | if (timeout) { |
1772 | hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS); |
1773 | if (!hrtimer_active(&timeout->timer)) |
1774 | timeout->task = NULL; |
1775 | } |
1776 | |
1777 | /* |
1778 | * If we have been removed from the hash list, then another task |
1779 | * has tried to wake us, and we can skip the call to schedule(). |
1780 | */ |
1781 | if (likely(!plist_node_empty(&q->list))) { |
1782 | /* |
1783 | * If the timer has already expired, current will already be |
1784 | * flagged for rescheduling. Only call schedule if there |
1785 | * is no timeout, or if it has yet to expire. |
1786 | */ |
1787 | if (!timeout || timeout->task) |
1788 | schedule(); |
1789 | } |
1790 | __set_current_state(TASK_RUNNING); |
1791 | } |
1792 | |
1793 | /** |
1794 | * futex_wait_setup() - Prepare to wait on a futex |
1795 | * @uaddr: the futex userspace address |
1796 | * @val: the expected value |
1797 | * @flags: futex flags (FLAGS_SHARED, etc.) |
1798 | * @q: the associated futex_q |
1799 | * @hb: storage for hash_bucket pointer to be returned to caller |
1800 | * |
1801 | * Setup the futex_q and locate the hash_bucket. Get the futex value and |
1802 | * compare it with the expected value. Handle atomic faults internally. |
1803 | * Return with the hb lock held and a q.key reference on success, and unlocked |
1804 | * with no q.key reference on failure. |
1805 | * |
1806 | * Returns: |
1807 | * 0 - uaddr contains val and hb has been locked |
1808 | * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked |
1809 | */ |
1810 | static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags, |
1811 | struct futex_q *q, struct futex_hash_bucket **hb) |
1812 | { |
1813 | u32 uval; |
1814 | int ret; |
1815 | |
1816 | /* |
1817 | * Access the page AFTER the hash-bucket is locked. |
1818 | * Order is important: |
1819 | * |
1820 | * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val); |
1821 | * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); } |
1822 | * |
1823 | * The basic logical guarantee of a futex is that it blocks ONLY |
1824 | * if cond(var) is known to be true at the time of blocking, for |
1825 | * any cond. If we locked the hash-bucket after testing *uaddr, that |
1826 | * would open a race condition where we could block indefinitely with |
1827 | * cond(var) false, which would violate the guarantee. |
1828 | * |
1829 | * On the other hand, we insert q and release the hash-bucket only |
1830 | * after testing *uaddr. This guarantees that futex_wait() will NOT |
1831 | * absorb a wakeup if *uaddr does not match the desired values |
1832 | * while the syscall executes. |
1833 | */ |
1834 | retry: |
1835 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ); |
1836 | if (unlikely(ret != 0)) |
1837 | return ret; |
1838 | |
1839 | retry_private: |
1840 | *hb = queue_lock(q); |
1841 | |
1842 | ret = get_futex_value_locked(&uval, uaddr); |
1843 | |
1844 | if (ret) { |
1845 | queue_unlock(q, *hb); |
1846 | |
1847 | ret = get_user(uval, uaddr); |
1848 | if (ret) |
1849 | goto out; |
1850 | |
1851 | if (!(flags & FLAGS_SHARED)) |
1852 | goto retry_private; |
1853 | |
1854 | put_futex_key(&q->key); |
1855 | goto retry; |
1856 | } |
1857 | |
1858 | if (uval != val) { |
1859 | queue_unlock(q, *hb); |
1860 | ret = -EWOULDBLOCK; |
1861 | } |
1862 | |
1863 | out: |
1864 | if (ret) |
1865 | put_futex_key(&q->key); |
1866 | return ret; |
1867 | } |
1868 | |
1869 | static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, |
1870 | ktime_t *abs_time, u32 bitset) |
1871 | { |
1872 | struct hrtimer_sleeper timeout, *to = NULL; |
1873 | struct restart_block *restart; |
1874 | struct futex_hash_bucket *hb; |
1875 | struct futex_q q = futex_q_init; |
1876 | int ret; |
1877 | |
1878 | if (!bitset) |
1879 | return -EINVAL; |
1880 | q.bitset = bitset; |
1881 | |
1882 | if (abs_time) { |
1883 | to = &timeout; |
1884 | |
1885 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? |
1886 | CLOCK_REALTIME : CLOCK_MONOTONIC, |
1887 | HRTIMER_MODE_ABS); |
1888 | hrtimer_init_sleeper(to, current); |
1889 | hrtimer_set_expires_range_ns(&to->timer, *abs_time, |
1890 | current->timer_slack_ns); |
1891 | } |
1892 | |
1893 | retry: |
1894 | /* |
1895 | * Prepare to wait on uaddr. On success, holds hb lock and increments |
1896 | * q.key refs. |
1897 | */ |
1898 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb); |
1899 | if (ret) |
1900 | goto out; |
1901 | |
1902 | /* queue_me and wait for wakeup, timeout, or a signal. */ |
1903 | futex_wait_queue_me(hb, &q, to); |
1904 | |
1905 | /* If we were woken (and unqueued), we succeeded, whatever. */ |
1906 | ret = 0; |
1907 | /* unqueue_me() drops q.key ref */ |
1908 | if (!unqueue_me(&q)) |
1909 | goto out; |
1910 | ret = -ETIMEDOUT; |
1911 | if (to && !to->task) |
1912 | goto out; |
1913 | |
1914 | /* |
1915 | * We expect signal_pending(current), but we might be the |
1916 | * victim of a spurious wakeup as well. |
1917 | */ |
1918 | if (!signal_pending(current)) |
1919 | goto retry; |
1920 | |
1921 | ret = -ERESTARTSYS; |
1922 | if (!abs_time) |
1923 | goto out; |
1924 | |
1925 | restart = ¤t_thread_info()->restart_block; |
1926 | restart->fn = futex_wait_restart; |
1927 | restart->futex.uaddr = uaddr; |
1928 | restart->futex.val = val; |
1929 | restart->futex.time = abs_time->tv64; |
1930 | restart->futex.bitset = bitset; |
1931 | restart->futex.flags = flags | FLAGS_HAS_TIMEOUT; |
1932 | |
1933 | ret = -ERESTART_RESTARTBLOCK; |
1934 | |
1935 | out: |
1936 | if (to) { |
1937 | hrtimer_cancel(&to->timer); |
1938 | destroy_hrtimer_on_stack(&to->timer); |
1939 | } |
1940 | return ret; |
1941 | } |
1942 | |
1943 | |
1944 | static long futex_wait_restart(struct restart_block *restart) |
1945 | { |
1946 | u32 __user *uaddr = restart->futex.uaddr; |
1947 | ktime_t t, *tp = NULL; |
1948 | |
1949 | if (restart->futex.flags & FLAGS_HAS_TIMEOUT) { |
1950 | t.tv64 = restart->futex.time; |
1951 | tp = &t; |
1952 | } |
1953 | restart->fn = do_no_restart_syscall; |
1954 | |
1955 | return (long)futex_wait(uaddr, restart->futex.flags, |
1956 | restart->futex.val, tp, restart->futex.bitset); |
1957 | } |
1958 | |
1959 | |
1960 | /* |
1961 | * Userspace tried a 0 -> TID atomic transition of the futex value |
1962 | * and failed. The kernel side here does the whole locking operation: |
1963 | * if there are waiters then it will block, it does PI, etc. (Due to |
1964 | * races the kernel might see a 0 value of the futex too.) |
1965 | */ |
1966 | static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect, |
1967 | ktime_t *time, int trylock) |
1968 | { |
1969 | struct hrtimer_sleeper timeout, *to = NULL; |
1970 | struct futex_hash_bucket *hb; |
1971 | struct futex_q q = futex_q_init; |
1972 | int res, ret; |
1973 | |
1974 | if (refill_pi_state_cache()) |
1975 | return -ENOMEM; |
1976 | |
1977 | if (time) { |
1978 | to = &timeout; |
1979 | hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME, |
1980 | HRTIMER_MODE_ABS); |
1981 | hrtimer_init_sleeper(to, current); |
1982 | hrtimer_set_expires(&to->timer, *time); |
1983 | } |
1984 | |
1985 | retry: |
1986 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE); |
1987 | if (unlikely(ret != 0)) |
1988 | goto out; |
1989 | |
1990 | retry_private: |
1991 | hb = queue_lock(&q); |
1992 | |
1993 | ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0); |
1994 | if (unlikely(ret)) { |
1995 | switch (ret) { |
1996 | case 1: |
1997 | /* We got the lock. */ |
1998 | ret = 0; |
1999 | goto out_unlock_put_key; |
2000 | case -EFAULT: |
2001 | goto uaddr_faulted; |
2002 | case -EAGAIN: |
2003 | /* |
2004 | * Task is exiting and we just wait for the |
2005 | * exit to complete. |
2006 | */ |
2007 | queue_unlock(&q, hb); |
2008 | put_futex_key(&q.key); |
2009 | cond_resched(); |
2010 | goto retry; |
2011 | default: |
2012 | goto out_unlock_put_key; |
2013 | } |
2014 | } |
2015 | |
2016 | /* |
2017 | * Only actually queue now that the atomic ops are done: |
2018 | */ |
2019 | queue_me(&q, hb); |
2020 | |
2021 | WARN_ON(!q.pi_state); |
2022 | /* |
2023 | * Block on the PI mutex: |
2024 | */ |
2025 | if (!trylock) |
2026 | ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1); |
2027 | else { |
2028 | ret = rt_mutex_trylock(&q.pi_state->pi_mutex); |
2029 | /* Fixup the trylock return value: */ |
2030 | ret = ret ? 0 : -EWOULDBLOCK; |
2031 | } |
2032 | |
2033 | spin_lock(q.lock_ptr); |
2034 | /* |
2035 | * Fixup the pi_state owner and possibly acquire the lock if we |
2036 | * haven't already. |
2037 | */ |
2038 | res = fixup_owner(uaddr, &q, !ret); |
2039 | /* |
2040 | * If fixup_owner() returned an error, proprogate that. If it acquired |
2041 | * the lock, clear our -ETIMEDOUT or -EINTR. |
2042 | */ |
2043 | if (res) |
2044 | ret = (res < 0) ? res : 0; |
2045 | |
2046 | /* |
2047 | * If fixup_owner() faulted and was unable to handle the fault, unlock |
2048 | * it and return the fault to userspace. |
2049 | */ |
2050 | if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) |
2051 | rt_mutex_unlock(&q.pi_state->pi_mutex); |
2052 | |
2053 | /* Unqueue and drop the lock */ |
2054 | unqueue_me_pi(&q); |
2055 | |
2056 | goto out_put_key; |
2057 | |
2058 | out_unlock_put_key: |
2059 | queue_unlock(&q, hb); |
2060 | |
2061 | out_put_key: |
2062 | put_futex_key(&q.key); |
2063 | out: |
2064 | if (to) |
2065 | destroy_hrtimer_on_stack(&to->timer); |
2066 | return ret != -EINTR ? ret : -ERESTARTNOINTR; |
2067 | |
2068 | uaddr_faulted: |
2069 | queue_unlock(&q, hb); |
2070 | |
2071 | ret = fault_in_user_writeable(uaddr); |
2072 | if (ret) |
2073 | goto out_put_key; |
2074 | |
2075 | if (!(flags & FLAGS_SHARED)) |
2076 | goto retry_private; |
2077 | |
2078 | put_futex_key(&q.key); |
2079 | goto retry; |
2080 | } |
2081 | |
2082 | /* |
2083 | * Userspace attempted a TID -> 0 atomic transition, and failed. |
2084 | * This is the in-kernel slowpath: we look up the PI state (if any), |
2085 | * and do the rt-mutex unlock. |
2086 | */ |
2087 | static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) |
2088 | { |
2089 | struct futex_hash_bucket *hb; |
2090 | struct futex_q *this, *next; |
2091 | struct plist_head *head; |
2092 | union futex_key key = FUTEX_KEY_INIT; |
2093 | u32 uval, vpid = task_pid_vnr(current); |
2094 | int ret; |
2095 | |
2096 | retry: |
2097 | if (get_user(uval, uaddr)) |
2098 | return -EFAULT; |
2099 | /* |
2100 | * We release only a lock we actually own: |
2101 | */ |
2102 | if ((uval & FUTEX_TID_MASK) != vpid) |
2103 | return -EPERM; |
2104 | |
2105 | ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE); |
2106 | if (unlikely(ret != 0)) |
2107 | goto out; |
2108 | |
2109 | hb = hash_futex(&key); |
2110 | spin_lock(&hb->lock); |
2111 | |
2112 | /* |
2113 | * To avoid races, try to do the TID -> 0 atomic transition |
2114 | * again. If it succeeds then we can return without waking |
2115 | * anyone else up: |
2116 | */ |
2117 | if (!(uval & FUTEX_OWNER_DIED) && |
2118 | cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0)) |
2119 | goto pi_faulted; |
2120 | /* |
2121 | * Rare case: we managed to release the lock atomically, |
2122 | * no need to wake anyone else up: |
2123 | */ |
2124 | if (unlikely(uval == vpid)) |
2125 | goto out_unlock; |
2126 | |
2127 | /* |
2128 | * Ok, other tasks may need to be woken up - check waiters |
2129 | * and do the wakeup if necessary: |
2130 | */ |
2131 | head = &hb->chain; |
2132 | |
2133 | plist_for_each_entry_safe(this, next, head, list) { |
2134 | if (!match_futex (&this->key, &key)) |
2135 | continue; |
2136 | ret = wake_futex_pi(uaddr, uval, this); |
2137 | /* |
2138 | * The atomic access to the futex value |
2139 | * generated a pagefault, so retry the |
2140 | * user-access and the wakeup: |
2141 | */ |
2142 | if (ret == -EFAULT) |
2143 | goto pi_faulted; |
2144 | goto out_unlock; |
2145 | } |
2146 | /* |
2147 | * No waiters - kernel unlocks the futex: |
2148 | */ |
2149 | if (!(uval & FUTEX_OWNER_DIED)) { |
2150 | ret = unlock_futex_pi(uaddr, uval); |
2151 | if (ret == -EFAULT) |
2152 | goto pi_faulted; |
2153 | } |
2154 | |
2155 | out_unlock: |
2156 | spin_unlock(&hb->lock); |
2157 | put_futex_key(&key); |
2158 | |
2159 | out: |
2160 | return ret; |
2161 | |
2162 | pi_faulted: |
2163 | spin_unlock(&hb->lock); |
2164 | put_futex_key(&key); |
2165 | |
2166 | ret = fault_in_user_writeable(uaddr); |
2167 | if (!ret) |
2168 | goto retry; |
2169 | |
2170 | return ret; |
2171 | } |
2172 | |
2173 | /** |
2174 | * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex |
2175 | * @hb: the hash_bucket futex_q was original enqueued on |
2176 | * @q: the futex_q woken while waiting to be requeued |
2177 | * @key2: the futex_key of the requeue target futex |
2178 | * @timeout: the timeout associated with the wait (NULL if none) |
2179 | * |
2180 | * Detect if the task was woken on the initial futex as opposed to the requeue |
2181 | * target futex. If so, determine if it was a timeout or a signal that caused |
2182 | * the wakeup and return the appropriate error code to the caller. Must be |
2183 | * called with the hb lock held. |
2184 | * |
2185 | * Returns |
2186 | * 0 - no early wakeup detected |
2187 | * <0 - -ETIMEDOUT or -ERESTARTNOINTR |
2188 | */ |
2189 | static inline |
2190 | int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb, |
2191 | struct futex_q *q, union futex_key *key2, |
2192 | struct hrtimer_sleeper *timeout) |
2193 | { |
2194 | int ret = 0; |
2195 | |
2196 | /* |
2197 | * With the hb lock held, we avoid races while we process the wakeup. |
2198 | * We only need to hold hb (and not hb2) to ensure atomicity as the |
2199 | * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb. |
2200 | * It can't be requeued from uaddr2 to something else since we don't |
2201 | * support a PI aware source futex for requeue. |
2202 | */ |
2203 | if (!match_futex(&q->key, key2)) { |
2204 | WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr)); |
2205 | /* |
2206 | * We were woken prior to requeue by a timeout or a signal. |
2207 | * Unqueue the futex_q and determine which it was. |
2208 | */ |
2209 | plist_del(&q->list, &hb->chain); |
2210 | |
2211 | /* Handle spurious wakeups gracefully */ |
2212 | ret = -EWOULDBLOCK; |
2213 | if (timeout && !timeout->task) |
2214 | ret = -ETIMEDOUT; |
2215 | else if (signal_pending(current)) |
2216 | ret = -ERESTARTNOINTR; |
2217 | } |
2218 | return ret; |
2219 | } |
2220 | |
2221 | /** |
2222 | * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2 |
2223 | * @uaddr: the futex we initially wait on (non-pi) |
2224 | * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be |
2225 | * the same type, no requeueing from private to shared, etc. |
2226 | * @val: the expected value of uaddr |
2227 | * @abs_time: absolute timeout |
2228 | * @bitset: 32 bit wakeup bitset set by userspace, defaults to all |
2229 | * @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0) |
2230 | * @uaddr2: the pi futex we will take prior to returning to user-space |
2231 | * |
2232 | * The caller will wait on uaddr and will be requeued by futex_requeue() to |
2233 | * uaddr2 which must be PI aware. Normal wakeup will wake on uaddr2 and |
2234 | * complete the acquisition of the rt_mutex prior to returning to userspace. |
2235 | * This ensures the rt_mutex maintains an owner when it has waiters; without |
2236 | * one, the pi logic wouldn't know which task to boost/deboost, if there was a |
2237 | * need to. |
2238 | * |
2239 | * We call schedule in futex_wait_queue_me() when we enqueue and return there |
2240 | * via the following: |
2241 | * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() |
2242 | * 2) wakeup on uaddr2 after a requeue |
2243 | * 3) signal |
2244 | * 4) timeout |
2245 | * |
2246 | * If 3, cleanup and return -ERESTARTNOINTR. |
2247 | * |
2248 | * If 2, we may then block on trying to take the rt_mutex and return via: |
2249 | * 5) successful lock |
2250 | * 6) signal |
2251 | * 7) timeout |
2252 | * 8) other lock acquisition failure |
2253 | * |
2254 | * If 6, return -EWOULDBLOCK (restarting the syscall would do the same). |
2255 | * |
2256 | * If 4 or 7, we cleanup and return with -ETIMEDOUT. |
2257 | * |
2258 | * Returns: |
2259 | * 0 - On success |
2260 | * <0 - On error |
2261 | */ |
2262 | static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, |
2263 | u32 val, ktime_t *abs_time, u32 bitset, |
2264 | u32 __user *uaddr2) |
2265 | { |
2266 | struct hrtimer_sleeper timeout, *to = NULL; |
2267 | struct rt_mutex_waiter rt_waiter; |
2268 | struct rt_mutex *pi_mutex = NULL; |
2269 | struct futex_hash_bucket *hb; |
2270 | union futex_key key2 = FUTEX_KEY_INIT; |
2271 | struct futex_q q = futex_q_init; |
2272 | int res, ret; |
2273 | |
2274 | if (!bitset) |
2275 | return -EINVAL; |
2276 | |
2277 | if (abs_time) { |
2278 | to = &timeout; |
2279 | hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ? |
2280 | CLOCK_REALTIME : CLOCK_MONOTONIC, |
2281 | HRTIMER_MODE_ABS); |
2282 | hrtimer_init_sleeper(to, current); |
2283 | hrtimer_set_expires_range_ns(&to->timer, *abs_time, |
2284 | current->timer_slack_ns); |
2285 | } |
2286 | |
2287 | /* |
2288 | * The waiter is allocated on our stack, manipulated by the requeue |
2289 | * code while we sleep on uaddr. |
2290 | */ |
2291 | debug_rt_mutex_init_waiter(&rt_waiter); |
2292 | rt_waiter.task = NULL; |
2293 | |
2294 | ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE); |
2295 | if (unlikely(ret != 0)) |
2296 | goto out; |
2297 | |
2298 | q.bitset = bitset; |
2299 | q.rt_waiter = &rt_waiter; |
2300 | q.requeue_pi_key = &key2; |
2301 | |
2302 | /* |
2303 | * Prepare to wait on uaddr. On success, increments q.key (key1) ref |
2304 | * count. |
2305 | */ |
2306 | ret = futex_wait_setup(uaddr, val, flags, &q, &hb); |
2307 | if (ret) |
2308 | goto out_key2; |
2309 | |
2310 | /* Queue the futex_q, drop the hb lock, wait for wakeup. */ |
2311 | futex_wait_queue_me(hb, &q, to); |
2312 | |
2313 | spin_lock(&hb->lock); |
2314 | ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); |
2315 | spin_unlock(&hb->lock); |
2316 | if (ret) |
2317 | goto out_put_keys; |
2318 | |
2319 | /* |
2320 | * In order for us to be here, we know our q.key == key2, and since |
2321 | * we took the hb->lock above, we also know that futex_requeue() has |
2322 | * completed and we no longer have to concern ourselves with a wakeup |
2323 | * race with the atomic proxy lock acquisition by the requeue code. The |
2324 | * futex_requeue dropped our key1 reference and incremented our key2 |
2325 | * reference count. |
2326 | */ |
2327 | |
2328 | /* Check if the requeue code acquired the second futex for us. */ |
2329 | if (!q.rt_waiter) { |
2330 | /* |
2331 | * Got the lock. We might not be the anticipated owner if we |
2332 | * did a lock-steal - fix up the PI-state in that case. |
2333 | */ |
2334 | if (q.pi_state && (q.pi_state->owner != current)) { |
2335 | spin_lock(q.lock_ptr); |
2336 | ret = fixup_pi_state_owner(uaddr2, &q, current); |
2337 | spin_unlock(q.lock_ptr); |
2338 | } |
2339 | } else { |
2340 | /* |
2341 | * We have been woken up by futex_unlock_pi(), a timeout, or a |
2342 | * signal. futex_unlock_pi() will not destroy the lock_ptr nor |
2343 | * the pi_state. |
2344 | */ |
2345 | WARN_ON(!&q.pi_state); |
2346 | pi_mutex = &q.pi_state->pi_mutex; |
2347 | ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1); |
2348 | debug_rt_mutex_free_waiter(&rt_waiter); |
2349 | |
2350 | spin_lock(q.lock_ptr); |
2351 | /* |
2352 | * Fixup the pi_state owner and possibly acquire the lock if we |
2353 | * haven't already. |
2354 | */ |
2355 | res = fixup_owner(uaddr2, &q, !ret); |
2356 | /* |
2357 | * If fixup_owner() returned an error, proprogate that. If it |
2358 | * acquired the lock, clear -ETIMEDOUT or -EINTR. |
2359 | */ |
2360 | if (res) |
2361 | ret = (res < 0) ? res : 0; |
2362 | |
2363 | /* Unqueue and drop the lock. */ |
2364 | unqueue_me_pi(&q); |
2365 | } |
2366 | |
2367 | /* |
2368 | * If fixup_pi_state_owner() faulted and was unable to handle the |
2369 | * fault, unlock the rt_mutex and return the fault to userspace. |
2370 | */ |
2371 | if (ret == -EFAULT) { |
2372 | if (rt_mutex_owner(pi_mutex) == current) |
2373 | rt_mutex_unlock(pi_mutex); |
2374 | } else if (ret == -EINTR) { |
2375 | /* |
2376 | * We've already been requeued, but cannot restart by calling |
2377 | * futex_lock_pi() directly. We could restart this syscall, but |
2378 | * it would detect that the user space "val" changed and return |
2379 | * -EWOULDBLOCK. Save the overhead of the restart and return |
2380 | * -EWOULDBLOCK directly. |
2381 | */ |
2382 | ret = -EWOULDBLOCK; |
2383 | } |
2384 | |
2385 | out_put_keys: |
2386 | put_futex_key(&q.key); |
2387 | out_key2: |
2388 | put_futex_key(&key2); |
2389 | |
2390 | out: |
2391 | if (to) { |
2392 | hrtimer_cancel(&to->timer); |
2393 | destroy_hrtimer_on_stack(&to->timer); |
2394 | } |
2395 | return ret; |
2396 | } |
2397 | |
2398 | /* |
2399 | * Support for robust futexes: the kernel cleans up held futexes at |
2400 | * thread exit time. |
2401 | * |
2402 | * Implementation: user-space maintains a per-thread list of locks it |
2403 | * is holding. Upon do_exit(), the kernel carefully walks this list, |
2404 | * and marks all locks that are owned by this thread with the |
2405 | * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is |
2406 | * always manipulated with the lock held, so the list is private and |
2407 | * per-thread. Userspace also maintains a per-thread 'list_op_pending' |
2408 | * field, to allow the kernel to clean up if the thread dies after |
2409 | * acquiring the lock, but just before it could have added itself to |
2410 | * the list. There can only be one such pending lock. |
2411 | */ |
2412 | |
2413 | /** |
2414 | * sys_set_robust_list() - Set the robust-futex list head of a task |
2415 | * @head: pointer to the list-head |
2416 | * @len: length of the list-head, as userspace expects |
2417 | */ |
2418 | SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head, |
2419 | size_t, len) |
2420 | { |
2421 | if (!futex_cmpxchg_enabled) |
2422 | return -ENOSYS; |
2423 | /* |
2424 | * The kernel knows only one size for now: |
2425 | */ |
2426 | if (unlikely(len != sizeof(*head))) |
2427 | return -EINVAL; |
2428 | |
2429 | current->robust_list = head; |
2430 | |
2431 | return 0; |
2432 | } |
2433 | |
2434 | /** |
2435 | * sys_get_robust_list() - Get the robust-futex list head of a task |
2436 | * @pid: pid of the process [zero for current task] |
2437 | * @head_ptr: pointer to a list-head pointer, the kernel fills it in |
2438 | * @len_ptr: pointer to a length field, the kernel fills in the header size |
2439 | */ |
2440 | SYSCALL_DEFINE3(get_robust_list, int, pid, |
2441 | struct robust_list_head __user * __user *, head_ptr, |
2442 | size_t __user *, len_ptr) |
2443 | { |
2444 | struct robust_list_head __user *head; |
2445 | unsigned long ret; |
2446 | const struct cred *cred = current_cred(), *pcred; |
2447 | |
2448 | if (!futex_cmpxchg_enabled) |
2449 | return -ENOSYS; |
2450 | |
2451 | if (!pid) |
2452 | head = current->robust_list; |
2453 | else { |
2454 | struct task_struct *p; |
2455 | |
2456 | ret = -ESRCH; |
2457 | rcu_read_lock(); |
2458 | p = find_task_by_vpid(pid); |
2459 | if (!p) |
2460 | goto err_unlock; |
2461 | ret = -EPERM; |
2462 | pcred = __task_cred(p); |
2463 | /* If victim is in different user_ns, then uids are not |
2464 | comparable, so we must have CAP_SYS_PTRACE */ |
2465 | if (cred->user->user_ns != pcred->user->user_ns) { |
2466 | if (!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE)) |
2467 | goto err_unlock; |
2468 | goto ok; |
2469 | } |
2470 | /* If victim is in same user_ns, then uids are comparable */ |
2471 | if (cred->euid != pcred->euid && |
2472 | cred->euid != pcred->uid && |
2473 | !ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE)) |
2474 | goto err_unlock; |
2475 | ok: |
2476 | head = p->robust_list; |
2477 | rcu_read_unlock(); |
2478 | } |
2479 | |
2480 | if (put_user(sizeof(*head), len_ptr)) |
2481 | return -EFAULT; |
2482 | return put_user(head, head_ptr); |
2483 | |
2484 | err_unlock: |
2485 | rcu_read_unlock(); |
2486 | |
2487 | return ret; |
2488 | } |
2489 | |
2490 | /* |
2491 | * Process a futex-list entry, check whether it's owned by the |
2492 | * dying task, and do notification if so: |
2493 | */ |
2494 | int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi) |
2495 | { |
2496 | u32 uval, uninitialized_var(nval), mval; |
2497 | |
2498 | retry: |
2499 | if (get_user(uval, uaddr)) |
2500 | return -1; |
2501 | |
2502 | if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) { |
2503 | /* |
2504 | * Ok, this dying thread is truly holding a futex |
2505 | * of interest. Set the OWNER_DIED bit atomically |
2506 | * via cmpxchg, and if the value had FUTEX_WAITERS |
2507 | * set, wake up a waiter (if any). (We have to do a |
2508 | * futex_wake() even if OWNER_DIED is already set - |
2509 | * to handle the rare but possible case of recursive |
2510 | * thread-death.) The rest of the cleanup is done in |
2511 | * userspace. |
2512 | */ |
2513 | mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED; |
2514 | /* |
2515 | * We are not holding a lock here, but we want to have |
2516 | * the pagefault_disable/enable() protection because |
2517 | * we want to handle the fault gracefully. If the |
2518 | * access fails we try to fault in the futex with R/W |
2519 | * verification via get_user_pages. get_user() above |
2520 | * does not guarantee R/W access. If that fails we |
2521 | * give up and leave the futex locked. |
2522 | */ |
2523 | if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) { |
2524 | if (fault_in_user_writeable(uaddr)) |
2525 | return -1; |
2526 | goto retry; |
2527 | } |
2528 | if (nval != uval) |
2529 | goto retry; |
2530 | |
2531 | /* |
2532 | * Wake robust non-PI futexes here. The wakeup of |
2533 | * PI futexes happens in exit_pi_state(): |
2534 | */ |
2535 | if (!pi && (uval & FUTEX_WAITERS)) |
2536 | futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); |
2537 | } |
2538 | return 0; |
2539 | } |
2540 | |
2541 | /* |
2542 | * Fetch a robust-list pointer. Bit 0 signals PI futexes: |
2543 | */ |
2544 | static inline int fetch_robust_entry(struct robust_list __user **entry, |
2545 | struct robust_list __user * __user *head, |
2546 | unsigned int *pi) |
2547 | { |
2548 | unsigned long uentry; |
2549 | |
2550 | if (get_user(uentry, (unsigned long __user *)head)) |
2551 | return -EFAULT; |
2552 | |
2553 | *entry = (void __user *)(uentry & ~1UL); |
2554 | *pi = uentry & 1; |
2555 | |
2556 | return 0; |
2557 | } |
2558 | |
2559 | /* |
2560 | * Walk curr->robust_list (very carefully, it's a userspace list!) |
2561 | * and mark any locks found there dead, and notify any waiters. |
2562 | * |
2563 | * We silently return on any sign of list-walking problem. |
2564 | */ |
2565 | void exit_robust_list(struct task_struct *curr) |
2566 | { |
2567 | struct robust_list_head __user *head = curr->robust_list; |
2568 | struct robust_list __user *entry, *next_entry, *pending; |
2569 | unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; |
2570 | unsigned int uninitialized_var(next_pi); |
2571 | unsigned long futex_offset; |
2572 | int rc; |
2573 | |
2574 | if (!futex_cmpxchg_enabled) |
2575 | return; |
2576 | |
2577 | /* |
2578 | * Fetch the list head (which was registered earlier, via |
2579 | * sys_set_robust_list()): |
2580 | */ |
2581 | if (fetch_robust_entry(&entry, &head->list.next, &pi)) |
2582 | return; |
2583 | /* |
2584 | * Fetch the relative futex offset: |
2585 | */ |
2586 | if (get_user(futex_offset, &head->futex_offset)) |
2587 | return; |
2588 | /* |
2589 | * Fetch any possibly pending lock-add first, and handle it |
2590 | * if it exists: |
2591 | */ |
2592 | if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) |
2593 | return; |
2594 | |
2595 | next_entry = NULL; /* avoid warning with gcc */ |
2596 | while (entry != &head->list) { |
2597 | /* |
2598 | * Fetch the next entry in the list before calling |
2599 | * handle_futex_death: |
2600 | */ |
2601 | rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); |
2602 | /* |
2603 | * A pending lock might already be on the list, so |
2604 | * don't process it twice: |
2605 | */ |
2606 | if (entry != pending) |
2607 | if (handle_futex_death((void __user *)entry + futex_offset, |
2608 | curr, pi)) |
2609 | return; |
2610 | if (rc) |
2611 | return; |
2612 | entry = next_entry; |
2613 | pi = next_pi; |
2614 | /* |
2615 | * Avoid excessively long or circular lists: |
2616 | */ |
2617 | if (!--limit) |
2618 | break; |
2619 | |
2620 | cond_resched(); |
2621 | } |
2622 | |
2623 | if (pending) |
2624 | handle_futex_death((void __user *)pending + futex_offset, |
2625 | curr, pip); |
2626 | } |
2627 | |
2628 | long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, |
2629 | u32 __user *uaddr2, u32 val2, u32 val3) |
2630 | { |
2631 | int ret = -ENOSYS, cmd = op & FUTEX_CMD_MASK; |
2632 | unsigned int flags = 0; |
2633 | |
2634 | if (!(op & FUTEX_PRIVATE_FLAG)) |
2635 | flags |= FLAGS_SHARED; |
2636 | |
2637 | if (op & FUTEX_CLOCK_REALTIME) { |
2638 | flags |= FLAGS_CLOCKRT; |
2639 | if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI) |
2640 | return -ENOSYS; |
2641 | } |
2642 | |
2643 | switch (cmd) { |
2644 | case FUTEX_WAIT: |
2645 | val3 = FUTEX_BITSET_MATCH_ANY; |
2646 | case FUTEX_WAIT_BITSET: |
2647 | ret = futex_wait(uaddr, flags, val, timeout, val3); |
2648 | break; |
2649 | case FUTEX_WAKE: |
2650 | val3 = FUTEX_BITSET_MATCH_ANY; |
2651 | case FUTEX_WAKE_BITSET: |
2652 | ret = futex_wake(uaddr, flags, val, val3); |
2653 | break; |
2654 | case FUTEX_REQUEUE: |
2655 | ret = futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0); |
2656 | break; |
2657 | case FUTEX_CMP_REQUEUE: |
2658 | ret = futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0); |
2659 | break; |
2660 | case FUTEX_WAKE_OP: |
2661 | ret = futex_wake_op(uaddr, flags, uaddr2, val, val2, val3); |
2662 | break; |
2663 | case FUTEX_LOCK_PI: |
2664 | if (futex_cmpxchg_enabled) |
2665 | ret = futex_lock_pi(uaddr, flags, val, timeout, 0); |
2666 | break; |
2667 | case FUTEX_UNLOCK_PI: |
2668 | if (futex_cmpxchg_enabled) |
2669 | ret = futex_unlock_pi(uaddr, flags); |
2670 | break; |
2671 | case FUTEX_TRYLOCK_PI: |
2672 | if (futex_cmpxchg_enabled) |
2673 | ret = futex_lock_pi(uaddr, flags, 0, timeout, 1); |
2674 | break; |
2675 | case FUTEX_WAIT_REQUEUE_PI: |
2676 | val3 = FUTEX_BITSET_MATCH_ANY; |
2677 | ret = futex_wait_requeue_pi(uaddr, flags, val, timeout, val3, |
2678 | uaddr2); |
2679 | break; |
2680 | case FUTEX_CMP_REQUEUE_PI: |
2681 | ret = futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1); |
2682 | break; |
2683 | default: |
2684 | ret = -ENOSYS; |
2685 | } |
2686 | return ret; |
2687 | } |
2688 | |
2689 | |
2690 | SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, |
2691 | struct timespec __user *, utime, u32 __user *, uaddr2, |
2692 | u32, val3) |
2693 | { |
2694 | struct timespec ts; |
2695 | ktime_t t, *tp = NULL; |
2696 | u32 val2 = 0; |
2697 | int cmd = op & FUTEX_CMD_MASK; |
2698 | |
2699 | if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || |
2700 | cmd == FUTEX_WAIT_BITSET || |
2701 | cmd == FUTEX_WAIT_REQUEUE_PI)) { |
2702 | if (copy_from_user(&ts, utime, sizeof(ts)) != 0) |
2703 | return -EFAULT; |
2704 | if (!timespec_valid(&ts)) |
2705 | return -EINVAL; |
2706 | |
2707 | t = timespec_to_ktime(ts); |
2708 | if (cmd == FUTEX_WAIT) |
2709 | t = ktime_add_safe(ktime_get(), t); |
2710 | tp = &t; |
2711 | } |
2712 | /* |
2713 | * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*. |
2714 | * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. |
2715 | */ |
2716 | if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || |
2717 | cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) |
2718 | val2 = (u32) (unsigned long) utime; |
2719 | |
2720 | return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); |
2721 | } |
2722 | |
2723 | static int __init futex_init(void) |
2724 | { |
2725 | u32 curval; |
2726 | int i; |
2727 | |
2728 | /* |
2729 | * This will fail and we want it. Some arch implementations do |
2730 | * runtime detection of the futex_atomic_cmpxchg_inatomic() |
2731 | * functionality. We want to know that before we call in any |
2732 | * of the complex code paths. Also we want to prevent |
2733 | * registration of robust lists in that case. NULL is |
2734 | * guaranteed to fault and we get -EFAULT on functional |
2735 | * implementation, the non-functional ones will return |
2736 | * -ENOSYS. |
2737 | */ |
2738 | if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) |
2739 | futex_cmpxchg_enabled = 1; |
2740 | |
2741 | for (i = 0; i < ARRAY_SIZE(futex_queues); i++) { |
2742 | plist_head_init(&futex_queues[i].chain); |
2743 | spin_lock_init(&futex_queues[i].lock); |
2744 | } |
2745 | |
2746 | return 0; |
2747 | } |
2748 | __initcall(futex_init); |
2749 |
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